15-04-2020 15:04 - edited 15-04-2020 15:05
This is actually back again.
I have a new phone and a new car, and it's back.
Changing the SIM resolves it in the short term, but there must be some mis-provisioning on my account or SIM card.
The only way to really resolve it is to invoke an IMSI/TMSI handshake again either by ejecting the SIM or restarting the phone.
Not sure how I could get this over to the right person at O2.